JP2013229965A - Energization circuit protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energization circuit protection device, capable of intercepting a conduction circuit by securely detecting heating in a circuit for controlling to drive a load by PWM driving a semiconductor switch.SOLUTION: When driving a load RL by PWM driving a semiconductor device 11 disposed in a circuit for connecting the load RL to a power supply VB, if a current flowing through the load RL exceeds a threshold temperature, the semiconductor device 11 is switched from PWM drive to DC drive. Thus, in the event of an overcurrent, an estimated temperature by temperature estimation means exceeds the threshold temperature and the semiconductor device 11 is intercepted, so that the energization circuit can surely be protected.

Description

  The present invention relates to a protection device for an energization circuit that immediately shuts off the circuit and protects the energization circuit when an overcurrent flows through an energization circuit that supplies power to a load mounted on a vehicle.

  A control device that controls a load mounted on a vehicle is equipped with a protection circuit in order to quickly shut down the circuit when an overcurrent flows through the load. As a conventional example of such a protection circuit, for example, one described in JP 2009-130944 A (Patent Document 1) is known. In Patent Document 1, the amount of heat generated and the amount of heat released from an energization circuit (wires and switches connecting a load and a power source) are calculated based on the value of current flowing through the load, and the ambient temperature is measured to determine the temperature of the energization circuit. It is disclosed that when the estimated temperature reaches a predetermined threshold, the energization circuit is cut off to protect the circuit connected to the load.

  However, in such a conventional protection circuit, when the semiconductor switch is PWM-controlled to drive a load, if there is an error in the estimated temperature, the semiconductor switch may not be properly cut off when the wire is heated. This will be described below with reference to the timing chart shown in FIG.

  In FIG. 4, (a) shows the sampling period for estimating the temperature, (b) shows the on / off timing of the semiconductor switch by PWM drive, and (c) shows the current flowing through the wire. Then, as shown by a curve P11, the wire temperature repeatedly rises during on-duty and falls during off-duty. That is, when the semiconductor switch is turned on, the wire temperature increases, and when the semiconductor switch is turned off, the wire temperature starts decreasing, and the wire temperature changes so as to repeat this.

  Here, if an error occurs in the estimation of the wire temperature, the estimated temperature may show a numerical value lower than the actual wire temperature, as shown by a curve P12 in FIG. 4, and the actual wire temperature (curve P11) is a threshold value. Although the temperature is above the temperature Tth, the estimated temperature (curve P12) may not exceed the threshold temperature Tth. In this case, the semiconductor switch cannot be shut off. For this reason, the problem that the temperature of an electric wire will exceed the threshold temperature Tth will generate | occur | produce.

JP 2009-130944 A

  As described above, in the conventional protection device for the energization circuit, the rising temperature and the falling temperature are obtained based on the current value flowing through the electric wire and the energizing time, and the electric wire temperature is estimated based on the rising temperature and the falling temperature. Therefore, when the load is driven by PWM control of the semiconductor switch, when the estimated temperature has an error, the semiconductor switch may be cut off even though the wire temperature exceeds the threshold temperature Tth. There was a problem that I could not.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to reliably detect heating of a circuit that controls driving of a load by PWM driving of a semiconductor switch. An object of the present invention is to provide a protective device for an energization circuit capable of interrupting the energization circuit.

  In order to achieve the above object, the invention according to claim 1 of the present application is an energization circuit protection device for protecting an energization circuit connecting a power source and a load from heat generation, and is provided in the energization circuit to drive and stop the load. A semiconductor switch for switching, a current detection means for detecting a current flowing in the energization circuit, a drive means for PWM driving the semiconductor switch when a drive input signal is given, a current flowing in the energization circuit, and an energization A temperature estimating means for estimating the electric wire temperature of the energizing circuit based on time, and outputting an off command to the semiconductor switch when the estimated temperature of the energizing circuit exceeds a preset threshold temperature by the temperature estimating means An abnormality determination unit that performs, and an overcurrent determination unit that determines whether or not a current value detected by the current detection unit exceeds a preset threshold current, Serial drive means, when the current value in the overcurrent determination means determines that exceeds the threshold current, and changes the semiconductor switch to the DC driven from PWM driving.

  According to a second aspect of the present invention, when the current value detected by the overcurrent determination unit exceeds a threshold current and then falls below the threshold current, the driving unit switches the semiconductor switch. The DC drive is returned to the PWM drive.

  In the protection device for the energization circuit according to the present invention, when the semiconductor switch provided in the circuit connecting the power source and the load is PWM driven to drive the load, when the current flowing through the load exceeds the threshold temperature, the semiconductor switch Is switched from PWM drive to DC drive. When an overcurrent occurs, the temperature estimated by the temperature estimating means exceeds the threshold temperature and the semiconductor switch is shut off, so that the energizing circuit can be reliably protected.

  In addition, when the value of the current flowing through the load falls below the threshold current, the semiconductor switch is controlled to switch from DC driving to PWM driving, so that it can be prevented from being affected by inrush current and noise when the switch is turned on. .

It is a circuit diagram which shows the structure of the load drive circuit containing the protection apparatus of the electricity supply circuit which concerns on one Embodiment of this invention. It is a flowchart which shows processing operation | movement of the protection apparatus of the electricity supply circuit which concerns on one Embodiment of this invention. It is a timing chart which shows the change of each signal of the protection device of the energization circuit concerning one embodiment of the present invention. It is a timing chart which shows the change of each signal of the protection device of the conventional energization circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Description of configuration]
FIG. 1 is a block diagram illustrating a configuration of a load driving device in which an energization circuit protection device according to an embodiment of the present invention is employed. As shown in FIG. 1, the load driving device 100 is provided between a power supply VB and a load RL, and controls a semiconductor device 11 that switches driving and stopping of the load, and controls on and off of the semiconductor device 11. The circuit 12 is configured.

  The semiconductor device 11 includes a semiconductor switch such as a MOSFET, for example, and operates by a PWM signal output from the control circuit 12 to supply power to the load RL. The semiconductor device 11 includes a current sensor 11 a such as a shunt resistor, and outputs a current signal detected by the current sensor 11 a to the control circuit 12.

  The control circuit 12 includes three connection terminals N1, N2, and N3 that are connected to external devices, and further includes a drive signal generation unit 21, a wire temperature estimation unit 22, an abnormality determination unit 23, and an overcurrent determination unit. 24, an inverting circuit 25, and an AND circuit 26.

  The drive signal generation unit 21 generates a PWM signal when an input signal is given from an external switch or the like, and outputs the generated PWM signal to the AND circuit 26. When a DC drive command signal is supplied from the overcurrent determination unit 24, the PWM signal is changed to a DC signal (DC signal), and this DC signal is output to the AND circuit 26.

  The electric wire temperature estimation unit 22 estimates the electric wire temperature of the energization circuit based on the current value detected by the current sensor 11a provided in the semiconductor device 11 and the energization time of the current by a method described later.

  The abnormality determination unit 23 outputs a temperature abnormality signal when the wire temperature estimated by the wire temperature estimation unit 22 exceeds a preset threshold temperature. That is, the output signal is changed from the “L” level to the “H” level. The inverting circuit 25 inverts the input signal and outputs it. That is, when the “H” level signal is output as the temperature abnormality signal from the abnormality determination unit 23, the signal is inverted to the “L” level and output.

  The overcurrent determination unit 24 outputs a DC drive command signal to the drive signal generation unit 21 when the current value detected by the current sensor 11a exceeds a preset threshold current.

  The AND circuit 26 outputs an “H” level output signal when both the output signal of the drive signal generator 21 and the output signal of the inverting circuit 25 are “H” level.

[Estimation process of wire temperature]
Next, the wire temperature estimation process in the above-described wire temperature estimation unit 22 will be described. First, calculation of the temperature rise will be described. When a current is flowing through the electric wire connected to the load RL, the energy (Pcin) consumed by the electric wire can be obtained from the following equation (1).

Pcin = rc × I2 (1)
However, rc is the conductor resistance [Ω] of the electric wire W1, and I is the energization current [A].

  Moreover, the energy (Pcout) discharged | emitted from an electric wire can be calculated | required by following (2) Formula.

Pcout = Qc (n-1) / (Cth × Rth) (2)
Here, Rth is the thermal resistance of the wire, Cth is the heat capacity of the wire, and Qc (n-1) is the amount of heat of the wire at the time of the previous sampling.

  Furthermore, by calculating these differences (Pcin−Pcout) based on the above formulas (1) and (2) and multiplying by the sampling time Δt, the heat generation amount or the heat dissipation amount of the wire during this sampling time can be determined. . Therefore, the amount of heat Qc (n) accumulated in the electric wire at the present time can be obtained by the following equation (3).

Qc (n) = Qc (n−1) + (Pcin−Pcout) × Δt (3)
Further, the rising temperature ΔT of the electric wire can be obtained by dividing the amount of heat Qc (n) obtained by the equation (3) by the heat capacity Cth of the electric wire. That is, the rising temperature ΔT is obtained by the following equation (4).

ΔT = Qc (n) / Cth (4)
The current estimated temperature T2 can be obtained by adding ΔT obtained by the equation (4) to the estimated temperature T1 (initially ambient temperature) obtained during the previous sampling time.

[Description of operation]
Next, the operation of the present embodiment configured as described above will be described with reference to the flowchart shown in FIG. First, in step S11 shown in FIG. 2, the drive signal generator 21 determines whether or not the input signal is on. If the input signal is off (NO in step S11), the drive signal is turned off in step S15. That is, the drive signal is not output (the output is set to “L” level).

  When the input signal is on (YES in step S11), the overcurrent determination unit 24 determines whether the current flowing in the electric wire exceeds the threshold current based on the current value detected by the current sensor 11a. Determine whether. If it is determined that no overcurrent is flowing (NO in step S12), an output command for the PWM signal is output to the drive signal generator 21 in step S13. That is, when the current flowing through the electric wire of the load circuit is a normal current, the semiconductor device 11 is PWM-controlled to drive the load RL.

  If it is determined that an overcurrent is flowing through the load circuit (YES in step S12), in step S14, the overcurrent determination unit 24 outputs a DC signal output command to the drive signal generation unit 21. As a result, the drive signal output from the drive signal generator 21 is switched from the PWM signal to the DC signal. As a result, the semiconductor device 11 is DC driven, that is, always turned on, and supplies power to the load RL.

  Next, the operation described above will be described with reference to the timing chart shown in FIG. 3A shows the sampling period of the control circuit 12, FIG. 3B shows the on / off signal of the semiconductor device 11, FIG. 3C shows the current value flowing through the load circuit, and FIG. The electric wire temperature estimated in the temperature estimation part 22 is shown.

  Now, when the PWM signal is output from the drive signal generation unit 21 and the semiconductor device is PWM-driven, the semiconductor device 11 is turned on as shown in FIG. 3B at time t1. Along with this, as shown in FIG. 3C, a current flows through the electric wire of the load circuit. At this time, if the value of the current flowing through the load circuit exceeds a preset threshold current Ith, it is detected by the overcurrent determination unit 24 shown in FIG. 1 that the drive signal generation unit 21 outputs The signal is changed from a PWM signal to a DC signal.

  Thereby, the semiconductor device 11 is DC-driven. Therefore, when the PWM drive is continued, the semiconductor device 11 is turned off at time t3, but is switched to DC drive, so that the on state is continued at time t3.

  On the other hand, the wire temperature estimation unit 22 starts the temperature estimation of the wire at time t2, which is a sampling period after time t1, and gradually increases the estimated temperature as shown in FIG. And even if the time t3 passes, the estimated temperature further rises and reaches the threshold temperature Tth at the time t4. As a result, the abnormality determination unit 23 detects a temperature abnormality of the electric wire and changes the output signal from the “L” level to the “H” level.

  As a result, the output signal of the AND circuit 26 is switched from the “H” level to the “L” level, and the semiconductor device 11 is turned off. As described above, when the overcurrent determination unit 24 detects that the value of the current flowing through the load circuit exceeds the threshold current Ith, the semiconductor device 11 is changed from PWM driving to DC driving. The electric wire temperature estimated by the part 22 continues to rise, reaches the threshold temperature Tth, and can shut off the semiconductor device 11.

  Further, when the current value detected by the current sensor 11a decreases and falls below the threshold current Ith, the overcurrent determination unit 24 changes the signal output to the drive signal generation unit 21 from the DC drive command to the PWM drive command. Since the change is made, the semiconductor device 11 is again switched to the PWM drive, and the load RL can be driven by a normal operation.

  In this manner, in the control device for the energization circuit according to the present embodiment, the current flowing through the energization circuit is detected by the current sensor 11a, and when the current value exceeds the threshold current Ith, the semiconductor device 11 is connected to the DC. Drive. Therefore, even when there is an error between the wire temperature estimated by the wire temperature estimation unit 22 and the actual wire temperature as in the conventional case, the estimated temperature of the wire increases with time, and the threshold value Since the temperature Tth is exceeded, the semiconductor device 11 can be reliably shut off, and the energization circuit and the load RL can be protected from heating.

  For this reason, for example, when a dead short occurs in the energization circuit, the estimated temperature of the electric wire is calculated and the semiconductor device 11 is shut off. Therefore, the energization circuit can be protected from heat generation due to the dead short.

  Further, since switching to DC driving is performed when an overcurrent flows, the number of times of switching of the semiconductor device 11 in the overcurrent state can be reduced, and damage to the device can be reduced.

  Further, after the semiconductor device 11 is changed to DC drive, if the current value decreases and falls below the threshold current Ith before the estimated temperature of the electric wire exceeds the threshold temperature Tth, the semiconductor device 11 is again set to PWM drive. Since it changes, it can return to normal driving. Therefore, when the semiconductor device 11 is turned on, it is not cut off by a short-time overcurrent such as noise or a short-time overcurrent such as noise. The semiconductor device 11 can be driven without any problem.

  The energization circuit protection device of the present invention has been described based on the illustrated embodiment, but the present invention is not limited to this, and the configuration of each part is an arbitrary configuration having the same function. Can be replaced.

  The present invention can be used to protect a circuit that drives a load from heating.

DESCRIPTION OF SYMBOLS 11 Semiconductor device 11a Current sensor 12 Control circuit 21 Drive signal generation part 22 Electric wire temperature estimation part 23 Abnormality determination part 24 Overcurrent determination part 25 Inversion circuit 26 AND circuit 100 Load drive device

Claims (2)

In the protection device for the energization circuit that protects the energization circuit that connects the power supply and the load from heat generation,
A semiconductor switch that is provided in the energization circuit and switches between driving and stopping of the load;
Current detecting means for detecting a current flowing in the energization circuit;
Drive means for PWM driving the semiconductor switch when a drive input signal is given;
A temperature estimating means for estimating the electric wire temperature of the energization circuit based on the current flowing through the energization circuit and the energization time;
An abnormality determining means for outputting an OFF command to the semiconductor switch when the estimated temperature of the energization circuit exceeds a preset threshold temperature by the temperature estimating means;
An overcurrent determination unit that determines whether or not a current value detected by the current detection unit exceeds a preset threshold current;
The energizing circuit protection device according to claim 1, wherein when the overcurrent determination unit determines that the current value exceeds a threshold current, the drive unit changes the semiconductor switch from PWM drive to DC drive.   The drive means returns the semiconductor switch from the DC drive to the PWM drive when the current value detected by the overcurrent determination means exceeds a threshold current and then falls below the threshold current. The energization circuit protection device according to claim 1.

Images